Guess I should have sent my answer by PM? I’m no gear head by any means, but as a petroleum chemist in love with any motor that’s out of the ‘norm’, I couldn’t restrain myself.

Just went to Wikipedia and discovered; “The bike became the most expensive production bike at the time when it was selling for $50,000 and with the rarity, they nowadays rarely change hands”. Hot bike with an amazingly different engine, that's a drool factor in my book.

Edit - Promise to share when I have a chance, to return to where stuff is in storage' to scan slide’s to show off pictures of a single cylinder wankel engine I made out of wood, not a running engine (of course) but a demonstrator only. Great waste of three months spare time twenty years ago.

The Honda Oval Piston Project started already in 1979 when Honda decided to return to road racing. Since the 500 class was dominated by two strokes Honda wanted to do a competitive four stroke. But simply speaking since the 4 cylinder two strokes fires every revolution Honda thought that they have to a V8 Four stroke to be competitive. This was anyhow forbidden according to the FIM rules so Honda thought that let us make almost a V8.

Oval pistons was not a a new idea. Already in the thirties some English companies tried the idea, but the problem to make piston rings were too big to overcome with that day’s technology. I cannot now find the name of the company but I remember that I saw a picture of the engine in a very old repair book for motorcycles (which I borrowed to somebody and on that trip the book is still)

Volkswagen tried in the 1980:s the same idea, together with Mahle, the piston manufacturer, and ended up with a 2.3 liter Diesel engine with oval pistons, presented in 1990. The project failed.

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VOLSKWAGEN OVAL ENGINE PROJECT.

When Ducati started their Moto Gp project they also started with the oval piston concept but abounded it and came up with a more traditional V4.

Anyhow Honda continued their project and finally they came out with the first NR500 a V4 racing machine with oval pistons. Mick Grant was riding it in the debut race at Silverstone (I think) and he crashed out and the whole machine went into flames and burned up. But Honda continued the project and stars like Freddie Spencer and Louis Capriossi rode the bike to decent places in the GP-races but never won any races, The NR 500 got a nickname Never Ready.

Then Honda realized that maybe in the Moto GP it is too difficult to compete, and anyhow Honda was successful with their NSR500 two strokers. Now they turned their eyes into Endurance, where the reliability of the NR engine together with an almost up to the edge power can make results, They put together a 750 version of the bike and in order to have it homologated they must make 200 bikes for the public. And they did.

In 1992 they presented the NR750 with a list price at factory at about 50,000 USD. The world’s most expensive bike.

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HONDA NR, THE WORLDS MOST EXPENSIVE MOTORCYCLE

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A BEAUTIFUL ENGINE PACKAGE

Because of the price the bike was mostly sold to celebrities and today the used bikes that are for sale costs between 60.000-100,000 USD. One bike is parked in Monte Carlo in the garage of Keke Rosberg the first Finish World champion in Formel 1 in 1982. He bought one from new. Yes it is the same family Rosberg that now races for Williams, His son Nico,who thus races on a German license.

The piston I posted is supposed to belong to a NR500 according the Honda page I copied it from. Anyhow I believe it belong to a NR750. As far as I know the NR500 had crankshafts with roller bearings in the crank shaft and the crank rods in the picture seems to have metal bearings and splitted crank rods. Who knows…

If you want to know more about this very expensive Honda adventure into oval piston design go to:

Attached Files:

What's the big advantage of oval pistons? Merely to make the engine more compact? - I'd understand the idea if Honda needed to beat the two-strokes in road racing, where every inch and ounce counts, but why would VW build a Diesel with oval pistons? There should be enough room in a sedan? Seems to me like the advantages don't justify the costs of development. Their VR engine was cheaper to build and more successful.

The idea with oval pistons is to make the engine more compact and to have a better "breathing" of the engine.The oval piston concept in the NR 750 allowed for eight valves per cylinder which generated more power due to the increased air/fuel mixture and compression. Anyhow at the end the NR engines didn't produce so much more power that it was worth the cost.